Structural and metabolic studies on several messenger ribonucleoprotein species will be carried out. Sites on the mRNA that are covered with proteins will be identified using cloned cDNA probes for these mRNAs. Possible changes in ribonucleoprotein structure that could be correlated with changes in actin mRNA stability in mouse ascites cells incubated in culture will be studied. Possible changes in structure and metabolism will also be examined in the mRNP for a stored mRNA species after activation of this species in the cells.